Sonar systems that transmit and receive sound with a sonar array are well known in the art. The sonar array can include one or more acoustic elements arranged in a pre-selected pattern, for example, a cylinder, a plane, a sphere, and/or a line.
The sonar system has both transmit functions and receive functions. The transmit functions include, but are not limited to, transmit beamforming. The receive functions include, but are not limited to, receive beamforming, target detection, target localization, target tracking, target display, and fire control solution processing, which can direct a weapon toward the target based upon the target localization and tracking.
With sonar arrays arranged as described above, transmit and receive beamforming techniques are known, which can form transmit beams associated with transmitted sound, and which can also form receive beams associated with received sound. In general, the transmit and the receive beams need not be identically shaped. Also, the transmit and the receive beams need not have the same shapes at different transmit and receive sound frequencies, even with the same sonar array.
It is known that transmit and receive beams, formed with a line array of acoustic elements, are symmetrical about the axis of the line array, and therefore, the beamforming can generate beams constrained in only one dimension (e.g., toroidal shaped beams). It is also known that transmit and receive beams formed with a planar arrangement of acoustic elements (e.g., a ring arrangement), or with a three dimensional arrangement of acoustic elements (e.g., a cylindrical arrangement), are shaped in two dimensions (e.g., a spotlight shaped beam).
Known beamforming techniques include time delay beamforming and phase shift beamforming. With time delay beamforming, for the transmit beamforming function, relative time delays are applied to transmit signals, which are sent to selected acoustic elements of the sonar array used for transmitting sound. For the receive beamforming function, relative time delays are applied to receive signals, which signals are generated by selected acoustic elements of the sonar array used for receiving sound, which are then added together. The relative time delays used in the transmit and receive functions need not be the same. Also, the acoustic elements selected to transmit sound need not be the same acoustic elements selected to receive sound. Also, the sonar array selected to transmit sound need not be in the same sonar array as the sonar array selected to receive sound.
The relative time delays control the steering of the transmit or receive beams. Therefore, by selecting the relative time delays, the transmit or receive beams, for example, the above-mentioned spotlight shaped beam, can be steered in two dimensions while generally maintaining its spotlight shape.
The transmit functions of a sonar system are characterized by a variety of performance characteristics, including but not limited to, a level of sound generated outside of a desired transmit beam (i.e., a transmit beam pattern sidelobe level), an accuracy with which the transmit beam can be pointed in a desired direction, and a desired output power of the transmit beam. The receive functions of a sonar system are also characterized by a variety of performance characteristics, including but not limited to, a receive noise floor, a level of sound received outside of a desired receive beam (i.e., a receive beam pattern sidelobe level), an accuracy with which the receive beam can be pointed in a desired direction, a target detection capability, a target localization accuracy, and a target tracking accuracy.
Conventional shipboard sonar systems used by the military generally include a plurality of racks of equipment, a group of which provides the above-described transmit functions (including transmit beamforming) and another group of which provide the above-described receive functions (including receive beamforming). In conventional sonar systems, the transmit and receive functions have been kept physically separated for a variety of reasons. One reason for separation of the transmit and receive functions is a perception that the transmit functions might generate crosstalk into the receive functions, resulting in degraded performance of the receive functions (i.e., a degraded receive noise floor). Another reason is power, wherein some of the transmit functions require more power than the receive functions, and therefore, power distribution is perceived to be easier if the transmit and receive functions are physically separated. Also, the control structure and control signals of conventional sonar systems are different for transmit and receive functions, resulting in a tendency to separate the transmit and receive functions. Furthermore, engineering disciplines and associated people who design electronic circuits for the transmit function and for the receive function of a conventional sonar system tend to be different.
The above-described physical separation of the transmit and receive functions of a conventional sonar system results in a large number of cables and cabinets. Notably, separate control cables are used for the transmit functions and for the receive functions.